Travail is more physical in that you may experience pain doing something that causes travail. Drudgery on the other hand is something that's just extremely boring. For example, reading a highly technical book can be a mental drudgery, but it's not travail because doing that does not cause you physical pain. Menial work that involves a lot of physical effort, however, is an example of travail.
Gosh, this book is such a drudgery! I just can't keep reading it anymore.
Factory workers in third-world countries are vastly underpaid while their hard work is nothing short of pure travail.